Basic Principles of Membrane Technology

Basic Principles of Membrane Technology

Basic Principles of Membrane Technology by Marcel Mulder Center for Membrane Science and Technology, University oftwente, Enschede, The Netherlands KLUWER ACADEMIC PUBLISHERS DORDRECHT I BOSTON I LONDON

A C.I.P. Catalogue record for this book is available from the Library of Congress ISBN-13: 978-0-7923-4248-9 DOl: 10.1007/978-94-009-1766-8 e-isbn -13: 978-94-009-1766-8 Published by Kluwer Academic Publishers, P.O. Box 17,3300 AA Dordrecht, The Netherlands. Kluwer Academic Publishers incorporates the publishing programmes of D. Reidel, Martinus Nijhoff, Dr W. Junk and MTP Press. Sold and distributed in the U.S.A. and Canada by Kluwer Academic Publishers, 101 Philip Drive, Norwell, MA 02061, U.S.A. In all other countries, sold and distributed by Kluwer Academic Publishers Group, P.O. Box 322, 3300 AH Dordrecht, The Netherlands. Printed on acid-free paper All Rights Reserved 1996 Kluwer Academic Publishers No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without written permission from the copyright owner.

CONTENTS I Introduction 1.1 Separation processes 1 1.2 Introduction to membrane processes 7 1.3 History 9 1.4 Definition of a membrane 12 1.5 Membrane processes 14 1.6 Solved problems 18 1.7 Unsolved problems 19 1.8 Literature 20 II Materials and material properties II. 1 Introduction 22 II.2 Polymers 22 II. 3 Stereoisomerism 24 II.4 Chain flexibility 26 II. 5 Molecular weight 27 II. 6 Chain interactions 29 II. 7 State of the polymer 31 II. 8 Effect of polymeric structure on Tg 33 II. 9 Glass transition temperature depression 40 II. 10 Thermal and chemical stability 41 II. II Mechanical properties 44 II. 12 Elastomers 45 II. 13 Thermoplastic elastomers 47 II. 14 Polyelectrolytes 47 II. 15 Polymer blends 49 II. 16 Membrane polymers 51 II. 16.1 Porous membranes 52 II. 16.2 Nonporous membranes 59 II. 17 Inorganic membranes 60 II. 17.1 Thermal stability 60 II. 17.2 Chemical stability 61 II. 17.3 Mechanical stability 61 II. 18 Biological membranes 62 II. 15.1 Synthetic biological membranes 66 II. 19 Solved problems 67 II.20 Unsolved problems 67 II. 21 Literature 69

III Preparation of synthetic membranes III. 1 Introduction 71 III.2 Preparation of synthetic membranes 72 III. 3 Phase inversion membranes 75 III. 3.1 Preparation by evaporation 76 III. 3.2 Precipitation. from the vapour phase 76 III. 3.3 Precipitation by controlled evaporation 76 III. 3.4 Thermal precipitation 76 III. 3.5 Immersion precipitation 77 III. 4 Preparation techniques for immersion precipitation 77 III. 4.1 Flat membranes 77 III. 4.2 Tubular membranes 78 III. 5 Preparation techniques for composite membranes 81 III. 5.1 Interfacial polymerisation 82 III. 5.2 Dip-coating 83 III. 5.3 Plasma polymerisation 86 III. 5.4 Modification of homogeneous dense membranes 87 III. 6 Phase separation in polymer systems 89 III. 6.1 Introduction 89 III. 6.1.1 Thermodynamics 89 III. 6.2 Demixing processes 99 III. 6.2.1 Binary mixtures 99 III. 6.2.2 Ternary systems 102 III. 6.3 Crystallisation 104 III. 6.4 Gelation 106 III. 6.5 Vitrification 108 III. 6.6 Thermal precipitation 109 III. 6.7 Immersion precipitation 110 III. 6.8 Diffusional aspects 114 III. 6.9 Mechanism of membrane formation 117 III. 7 Influence of various parameters on membrane morphology 123 III. 7.1 Choice of solvent-nonsolvent system 123 III. 7.2 Choice of the polymer 129 III. 7.3 Polymer concentration 130 III. 7.4 Composition of the coagulation bath 132 III. 7.5 Composition of the casting solution 133 III. 7.6 Preparation of porous membranes - summary 134 III. 7.7 Formation of integrally skinned membranes 135 III. 7.7.1 Dry-wet phase separation process 136 III. 7.7.2 Wet-phase separation process 137 III. 7.8 Formation of macrovoids 138 III. 8 Inorganic membranes 141 III. 8.1 The sol-gel process 141 III. 8.2 Membrane modification 144 III. 8.3 Zeolite membranes 144 III. 8.4 Glass membranes 146 III. 8.5 Dense membranes 147 I1I.9 Solved problems 147

III. 10 Unsolved problems 147 III. 11 Literature 154 IV Characterisation of membranes IV.1 Introduction 157 IV.2 Membrane characterisation 158 IV.3 Characterisation of porous membranes 160 IV.3.1 Microfiltration 162 IV. 3.1.1 Electron microscopy 162 IV.3.l.2 Atomic force microscopy 164 IV. 3.1.3 Bubble-point method 165 IV. 3.1.4 Bubble-point with gas permeation 167 IV. 3.1.5 Mercury intrusion method 16)\ IV. 3.1.6 Permeability method 169 IV.3.2 Ultrafiltration 172 IV. 3.2.l. Gas adsorption-desorption 173 IV. 3.2.2 Thermoporometry 176 IV. 3.2.3 Permporometry 179 IV. 3.2.4 Liquid displacement 181 IV. 3.2.5 Solute rejection measurements 183 IV.4 Characterisation of ionic membranes 188 IV.4.1 Electrokinetic phenomena 189 IV.4.2 Electro-osmosis 192 IV.5 Characterisation of nonporous membranes 192 IV.5.1 Permeability methods 194 IV.5.2 Physical methods 195 IV. 5.2.1 DCSJDTA methods 195 IV. 5.2.2 Density measurements 197 IV. 5.2.2.1 Density gradient column 197 IV. 5.2.2.2 Density determination by the Archimedes principle 198 IV. 5.2.3 Wide-angle X-ray diffraction (W AXD) 198 IV.5.3 Plasma etching 199 IV. 5.4 Surface analysis methods 201 IV.6 Solved problems 204 IV.7 Unsolved problems 204 IV.8 Literature 208 V Transport in membranes V.l Introduction 210 V.2 Driving forces 212 V.3 Nonequilibrium thermodynamics 214 V.4 Transport through porous membranes 224 V.4.1 Transport of gases through porous membranes 225 V. 4.1.1 Knudsen flow 226 V.4.2 Friction model 228

V.5 Transport through nonporous membranes 232 V.5.1 Transport in ideal systems 239 V.5.1.1 Determination of the diffusion coefficient 243 V.5.1.2 Determination of the solubility coefficient 244 V. 5.1.3 Effect of temperature on the permeability coefficient 246 V.5.2 Interactive systems 248 V.5.2.1 Free volume theory 251 V.5.2.2 Clustering 254 V.5.2.3 Solubility of liquid mixtures 255 V. 5.2.4 Transport of single liquids 257 V.5.2.5 Transport of liquid mixtures 258 V.5.3 Effect of crystallinity 259 V.6 Transport through membranes. A unified approach 260 V. 6.1 Reverse osmosis 264 V.6.2 Dialysis 266 V.6.3 Gas permeation 266 V. 6.4 Pervaporation 267 V.7 Transport in ion-exchange membranes 267 V.8 Solved problems 271 V.9 Unsolved problems 272 V.8 Literature 278 VI Membrane processes VI. 1 Introduction 280 VI. 2 Osmosis 282 VI. 3 Pressure driven membrane processes 284 VI.3.1 Introduction 284 VI.3.2 Microfiltration 286 VI. 3.2.1 Membranes for microfiltration 288 VI. 3.2.2 Industrial applications 292 VI. 3.2.3 Summary of micro filtration 292 VI.3.3 Ultrafiltration 293 VI. 3.3.1 Membranes for ultrafiltration 294 VI. 3.3.2 Applications 295 VI. 3.3.3 Summary of ultrafiltration 296 VI. 3.4 Reverse osmosis and nanofiltration 297 VI. 3.4.1 Membranes for reverse osmosis and nanofiltration 299 VI. 3.4.2 Applications 301 VI. 3.4.3 Summary of nanofiltration 302 VI. 3.4.3 Summary of reverse osmosis 303 VI.3.5 Pressure retarded osmosis 303 VI. 3.5.1 Summary of pressure retarded osmosis 305 VI.3.6 Piezodial ysis 305 VI. 3.6.1 Summary of piezodialysis 306 VI. 4 Concentration as driving force 307 VI.4.1 Introduction 307 VI.4.2 Gas separation 308

VI.4.2 Gas separation 308 VI. 4.2.1 Gas separation in porous membranes 308 VI.4.2.2 Gas separation in nonporous membranes 309 VI.4.2.3 Aspects of separation 311 VI. 4.2.4 louie - Thomson effect 317 VI. 4.2.5 Membranes for gas separation 319 VI. 4.2.6 Applications 323 VI. 4.2.7 Summary of gas separation 324 VI.4.3 Pervaporation 325 VI.4.3.1 Aspects of separation 327 VI. 4.3.2 Membranes for pervaporation 333 VI. 4.3.3 Applications 336 VI. 4.3.4 Summary of pervaporalion 339 VI. 4.4 Canier mediated transport 339 VI. 4.4.1 Liquid membranes 340 VI. 4.4.2 Aspects of separation 347 VI. 4.4.3 Liquid membrane development 352 VI. 4.4.4 Choice of the organic solvent 353 VI. 4.4.5 Choice of the carrier 355 VI. 4.4.6 Applications 357 VI. 4.4.7 Summary of carrier mediated transport 357 VI.4.5 Dialysis 358 VI. 4.5.1 Transport 359 VI. 4.5.2 Membranes 360 VI. 4.5.3 Applications 360 VI. 4.5.4 Summary of dialysis 361 VI.4.6 Diffusion dialysis 361 VI.4.6.1 Applications 363 VI. 4.6.2 Summary of diffusion dialysis 364 VI. 5 Thermally driven membrane processes 364 VI.5.1 Introduction 364 VI.5.2 Membrane distillation 365 VI. 5.2.1 Process parameters 367 VI. 5.2.2 Membranes 370 VI. 5.2.3 Applications 370 VI. 5.2.4 Summary of membrane distillation 373 VI. 6 Membrane contactors 373 VI.6.1 Gas-liquid contactor 375 VI. 6.1.1 Introduction 375 VI.6.2 Liquid-liquid contactors 377 VI. 6.2.1 Introduction 377 VI.6.3 Nonporous membrane contactors 378 VI. 6.4 Summary of membrane contactors 379 VI.6.5 Thermo-osmosis 380 VI.7 Electrically driven membrane processes VI.7.1 Introduction 380 VI.7.2 Electrodialysis 380 VI. 7.2.1 Process parameters 382 VI. 7.2.2 Membranes for electrodialysis 385

VI. 8 VI. 9 VI. 10 VI. II VI. 7.2.3 Applications 387 VI. 7.2.3.1 Separation of amino acids 387 VI. 7.2.4 Summary of electrodialysis 388 VI. 7.3 Membrane electrolysis 388 VI.7.3.1 The 'chlor-alkali' process 3119 VI. 7.3.2 Bipolar membranes 390 VI. 7.4 Fuel cells 391 VI. 7.5 Electrolytic regeneration of mixed-bed ion-exchange resin 393 Membrane reactors and membrane bioreactors 394 VI. 8.1 Membrane reactors 395 VI. 8.2 Non-selective membrane reactor 396 VI. 8.3 Membrane reactor in liquid phase reactions 398 VI. 8.4 Membrane bioreactors 400 Solved problems 400 Unsolved problems 402 Literature 412 VII Polarisation phenomena and fouling VII. 1 VII.2 VII.3 VII.4 VII.5 VII.6 VII.7 VII.8 VII.9 VII. 10 VII. 11 VII. 12 VII. 13 VII. 14 VII. 15 VII. 16 VII. 17 Introduction Concentration polarisation VII. 2.1 Concentration profiles Turbulence promoters Pressure drop Characteristic nux behaviour in pressure driven membrane operations Gel layer model Osmotic pressure model Boundary layer resistance model Concentration polarisation in diffusive membrane separations Concentration polarisation in electrodialysis Temperature polarisation Membrane fouling VII.12.1 Fouling tests in reverse osmosis Methods to reduce fouling Compaction Solved problems Unsolved problems Literatw'e 416 418 423 424 426 427 429 431 436 440 442 444 447 451 453 456 456 457 463 VIII Module and process design VIII. 1 VIII. 2 VIII. 3 VIII. 4 VIII. 5 VIII. 6 Introduction Plate-and-frame model Spiral wound module Tubular module Capillary module Hollow fiber module 465 466 468 469 470 472

VIII. 7 VIII. 8 VIII. 9 VIII. 10 VIII. 11 VIII. 12 VIII. 13 VIII. 14 VIII. IS VIII. 16 VIII. 17 VIII. 18 VIII. 19 VIII. 20 VIII. 21 VlIl. 22 VIII. 23 Appendix I Appendix 2 Comparison of the module configurations System design Cross-flow operations Hybrid dead-end/cross flow system Cascade operations Some examples of system design VIII. 12.1 Ultrapure water VIII. 12.2 Recovery of organic vapours VIII. 12.3 Desalination of seawater VIII. 12.4 Dehydration of ethanol VIII. 12.5 Economics Process parameters Reverse osmosis Diafiltration Gas separation and vapour permeation VIII. 16.1 Gas separation under complete mixing conditions VIII. 16.2 Gas separation under cross-flow conditions Pervaporation VIII. 17.1 Complete mixing in pervaporation VIII. 17.2 Cross-flow in pervaporation Pervaporation Dialysis Energy requirements VIn. 20.1 Pressure driven processes VIII. 20.2 Partial pressure driven processes VIII. 20.3 Concentration driven processes Solved problems Unsolved problems Literature 473 474 475 478 479 480 481 482 483 484 485 486 487 491 493 494 496 498 498 500 501 503 505 506 507 508 509 511 519 522 523 Answers to exercises: solved problems Answers to exercises: unsolved problems List of symbols Index 525 547 553 557

Preface Membranes playa central role in our daily life, or as indicated by one of my foreign colleagues, Richard Bowen, 'If you are tired of membranes, you are tired of life'. Biological membranes are hardly used in industrial applications, but separations with synthetic membranes have become increasingly important. Today, membrane processes are used in a wide range of applications and their numbers will certainly increase. Therefore, there is a need for well educated and qualified engineers, chemists, scientists and technicians who have been taught the basic principles of membrane technology. However, despite the growing importance of membrane processes, there are only a few universities that include membrane technology in their regular curricula. One of the reasons for this may be the lack of a comprehensive textbook. For me, this was one of the driving forces for writing a textbook on the basic principles of membrane technology which provides a broad view on the various aspects of membrane technology. I realise that membrane technology covers a broad field but nevertheless I have tried to describe the basic principles of the various disciplines. Although the book was written with the student in mind it can also serve as a first introduction for engineers, chemists, and technicians in all kind of industries who wish to learn the basics of membrane technology. The book is divided into eight chapters, each covering a basic topic: Chapter I is an introduction to the field and gives some definitioi),s and the historical development. Chapter 2 is a survey of polymers used as membrane material and describes the factors that determine the material properties. Chapter 3 gives an overview of various preparation techniques. Most of the commercial available membranes are prepared by phaseinversion and this technique will be d~scribed in detail. Chapter 4 describes all kind of characterisation techniques, both for porous membranes as well as for nonporous membranes. Transport across a membrane occurs when a driving force is applied. Different types of driving forces can be applied and are described in chapter 5. Also membrane transport is described in this chapter. Chapter 6 gives a survey of various technical membrane processes. These processes are classified according to their driving forces. Concentration polarisation is a phenomenon which is inherently related to membrane separation. Description of this phenomenon and of fouling are given in chapter 7. Finally, in chapter 8 the basic aspects of module and process design are described. At the end of this chapter some process calculations are given. Let me conclude by acknowledging the many who helped me writing this book. I am pleased to say that they are all (former) members of our membrane research group at the University of Twente. My first experience with membrane technology was in 1974 when I entered this university. Membrane research had just started at that time initiated by the promising expectations from the activities of the Office of Saline Water in the USA. Since then, the research activities have grown and at this moment membrane technology is one of the main research topics in our faculty, with more than 70 researchers being active in various fields. In 1980, we started a graduate course on membrane technology for chemical engineering students. Since then, the course has heen extended and improved. All my colleagues who contributed to the course also contributed directly or indirectly to helping me write this book. I am specially indebted to Kees Smolders, the driving force behind membrane research at our

University, who is always very dynamic, enthusiastic and stimulating. Other colleagues of the beginning period were Frank Altena and Maarten van der Waal. Since then a nl!mber of people have been involved in the membrane course: Hans Wijmans, Hans van den Berg, Hans Wesselingh, Matthias Wessling, Heiner Strathmann, Thonie van den Boomgaard, and Gert van den Berg. I would like to thank all these colleagues who added substantially to this book. Furthermore, I wish to thank Zandrie Borneman who made a number of the scanning electron micrographs and Ingo Blume, who has critically read the manuscript and suggested corrections. Errors that remain are my fault. It was also Ingo Blume who designed the cover and Willem Puper who drew the Maxwell demon. Especially, I wish to acknowledge my wife Ios for her patience and understanding during the many hours in the evenings when I was writing the book. Finally, I wish to express my warm feelings to my sons Ivo and Ioris for just being there. Marcel Mulder, April 1991 Preface to second edition Membrane technology is increasingly expanding and the number of people dealing with membranes is growing rapidly. Most applications refer to concentration, purification and fractionation. However, in the last decade much research has been devoted to membrane reactors (and membrane bioreactors), the combination of a chemical reaction with a membrane separation process to shift the equilibrium or Lo provide in a better way the reactants that a higher productivity is obtained. New materials and membranes are required in which catalytic activity has been incorporated but there is still a long way to go. Some aspects of membrane reactors are described in chapter VI. Also membrane contactors, in which the membrane acts as an interphase, are described now, at least some basic principles. The major difference with the first edition is the incorporation of problems. It was said in one of the book reviews, 'problems should be a part of a (any) textbook' and I agree with that. I want to thank all the people from all places around the world for their comments, considerations and positive reactions. This makes it worth to put so many hours in writing and up-dating the book and it helped me to finalize the second edition. Marcel Mulder, May 1996